I booked through rentalcars a car with Avis. I read the terms and conditions and was familiar that there might be an additional charge on the petrol, depending on the arrangement. At the car pick up, the agent told me we will make the contract that I return the car with full tank therefore no extra cost - he put on the contract fuel prepaid. I did so, returned the car with full tank and several days after the return, I was charged with an extra 60 EUR (more than contractually possible and definitely not a fuel "pre-pay" in my definition).
I called several times, wrote my complaint in April, sent several reminders...no one ever replied to me. The fact that they charged me contrary to what they said was rude, the fact they didn't bother even answering for two months was completely unprofessional, especially for a rent-a-car agency from a global franchize. So, avoid at any cost!